The constraint on habitat use in wing-moulting Greylag Geese Anser anser caused by anti-predator displacements

During the flightless period of wing-moult, terrestrial feeding waterbirds tend to forage close to water. Wing-moulting Greylag Geese Anser anser feeding in a Danish saltmarsh were no exception to this pattern as none fed more than 175 m from the sea. An individual-based stochastic model of goose feeding distribution derived from empirical data showed that requirements for drinking water could not explain the coastal feeding distribution as the model predicted that 57% of all goose observations would be more than 175 m from the sea. The availability of Common Saltmarsh Grass Puccinellia maritima , the preferred food item, could partly explain the exploitation pattern of geese but not the absence of geese from inland feeding areas. Furthermore, the results did not support the hypothesis that geese actively avoided inland feeding areas because of elevated costs from vigilance. The frequency of anti-predator displacement to the sea was the most likely explanation of the feeding pattern. A model that included such displacements predicted that 99% of all geese would feed less than 175 m from the sea. As anti-predator displacement put the most severe constraints on the feeding distribution, predation risk and level of disturbance were suggested to be the overall factors, which determine the choice of moult site in wing-moulting geese.